Froth flotation apparatus



Dec. 11, 1951 Filed Aug. 13, 1948 PAYNE 2,577,802

FROTH FLOTATION APPARATUS 2 SHEETSSHEET l Fig. 1

INI/E/VTUP PEARSON M B4Y/Vf ATTORNEY Dec. 11, 1951 PAYNE 2,577,802

FROTH FLOTATION APPARATUS Filed Aug. 15, 1948 2 SHEETS-SHEET 2 INVENTORV PEARSON M. PAYNE ATTORNEY Patented Dec. 11, 1951 UNITED STATES PATENTOFFICE 3 Claims.

This invention relates to the processes and techniques of frothflotation, and more particularly to such processes and techniquesapplied to the selective separation of comminuted, intermixed materials,and has as an object to provide a novel and improved method for thepractical development and effective application of known flotativeprinciples.

A further object of the invention is to provide novel and improvedtypical apparatus susceptible of embodiment in a variety of specificforms for the efficient practice of froth flotation methods.

A further object of the invention is to provide an improved type ofimpeller efiiciently operable for the froth flotative aeration of liquidpulps.

A further object of the invention is to provide an improved frothflotation method marked by effective pulp aeration consequent directlyand H solely upon impeller actuation.

A further object of the invention is to provide improved froth flotationmethods and means applicable with enhanced efficiency to separationsaccomplished through either intermittent-flow, cell type orcontinuous-flow, trough type pulp receivers.

A further object of the invention is to provide improved froth flotationmethods and means susceptible of ready adaptation, with or withoutprocess interruption, to efficiently meet the operative requirementscharacteristic of a given flotative separation.

A further object of the invention is to provide improved froth flotationmethods and means characterized by low initial, operating, andmaintenance costs, simplicity and flexibility of application toeflicient resolution of particular separatory problems, highadaptability, and maximum effectiveness in the practical adaptation ofknown pertinent principles to culmination in desired end results.

With the foregoing and other objects in view,

Figure 1 is a side elevation, partly in vertical section, of one simpleembodiment of the principles of the invention as applied to and forcooperation with a conventional froth flotation cell. Figure 2 is afragmentary, detail section verti cally through a modification adaptableto use -"-generation and enhance the persistence of the bubbles to theultimate development of a relatively deep froth bed built up above andremovable from the pulp body, and the same, or other, reagents exercisetheir selective affinity for pulp solids to entrain such solids into thefroth bed whence they may be recovered as an isolated fraction of thepulp body. Conventional methods and apparatus for the practicalapplication of froth flotation principles utilize impeller-typeagitators of excessive mass requiring high power input for theiractuation, are characterized by complications incident to adequate airsupply to and through such agitators, and are exceedingly difficult,ifnot Wholly impractical, or adaptation to successful separations from acontinuous ciples in a manner and through means obviating theshortcomings and disadvantages of the hithquacy of a continuing supplyof small-size buberto-known techniques.

Quite obviously, the effectiveness of separation by means of frothflotation is to a large degree proportional to the pulp agitation andthe adebles throughout the full depth of the pulp body, and it isapparent that efliciency of the separatory operation is served when therequisite agitation may be had through an instrumentality of "'smallmass and low operating resistance and at the same time adequate aerationof the pulp body results directly from the actuation of such agitatinginstrumentality, and from such considerations derive the novel featuresand operating relationships of the instant invention.

Replacing the large-mass conventional impellers disposed for agitatingeffect in the lower zones of the pulp body and designed to expelaxially-indrawn, or otherwise supplied, air to 3 and only within theirzones of agitation, the method of the invention is given effect by meansof a whip-type impeller whereof the agitating elements cut the surfaceof the pulp body in a manner to positively entrain air from above andthrough said surface to effect bubble generation through the entire pulpbody depth as a direct and immediate consequence of the pulp-agitatingimpeller actuation. Various structural arrangements and combinations,certain of which are illustrated, supply the operative characteristicsabove set forth and adapt the invention to particular environments andapplications. In Figure l, a conventional flotation cell iii ofgenerally rectangular type, which may be one of an intercommunicatingbattery of like units, is

shown as provided with the usual lowered Wall margin forming a lip I6 ator slightly above the level of the pulp body top surface whereover frothfrom the bed developed on and above the pulp body may flow or bedeflected with its entrapped material to recovery of the latter apartfrom the pulp wherefrom it has been separated. Any suitable fixedsupport, such as a beam i'l bridging the'top of the cell, rigidly oradjustably mounts a journal bearing l8 in spaced relation above the cellwith its bore axis directed preferably centrally and perpendicular tothe top plane of the cell charge, and a shaft 19 is rotatably carried bythe bearing is in suitable driven relation with a source of power, suchas an electric motor 20 either adjacent or remote from said shaft andits bearing. The shaft i2 is held against reciprocation axially of thebearing it and terminates near the top plane of the normal cell chargewhere it fixedly mounts a radially-extending, annular flange, or head,2% from which a plurality of like whip elements 22 fixedly projectdownwardly of the cell if: in a uniform spacing angularly about theflange 2i and a uniform downward divergence away from the axis of shaftl9 rotation as a conical assembly coaxial with said shaft andcharacterized by an open base adjacent the floor of the cell E5. Thewhips 22 are preferably straight, rod-like elements, circular insection, of any suitable material having the requisite properties ofresilient stiffness and resistance to abrasion, and, as represented inFigure 8, said whips may be solid cylinders, or, alternatively, they maybe tubular elements open at each end, as indicated in Figure 7.Assembled and mounted as shown and described, the whips Z2 rotate withthe shaft I9 as the latter is power-actuated to successively open andfollow a conical orbit through the cell charge, the lower, free ends ofsaid whips, by virtue of the whip divergence from the axis of rotation,travelling at a linear speed greater than that of their upper ends.Rotation of the whip assembly within the cell charge is productive ofagitation and consequent charge turbulence which increases as the speedof assembly rotation is increased up to a certain maximum, dependent tosome extent upon the nature and density of the cell charge, beyond whichincreased speed of assembly rotation may be marked by a decrease incharge agitation, it being hence feasible to regulate the degree ofcharge agitation through control of the shaft I9 speed of rotation. Ateven moderate speeds of 7 whip assembly rotation, a vortex is formed inthe cases where said whip upper ends were submerged in a quiescentcharge, so that the forces generated by rotation of the whip assemblythrough the cell charge may act to entrain air from above the chargelevel rearwardly of and longitudinally along each whip 22 todissemination through the charge as an infinity of smallsize bubbles ina continuing process of generation along each whip length to and injetted relation from the whip free ends. Manifestly, rapid transit ofeach whip 22 through the cell charge is productive of eddy currents anda region of reduced pressure in immediate trailing relation therewith,through which region air at atmospheric pressure is impelled to enterand become subject to the eddy currents, while the centrifugal forces ofassembly rotation as modified by the whip inclination relative to theaxis of rotation tend to entrain the air to the whip free ends and atthe same time break up and disseminate the air flow for intensegeneration of desired small-size bubbles. Whatever may be a correctanalysis of the forces, and the bubblegenerating coaction thereof,incident to whip assembly rotation within the cell charge, it is anobservable phenomenon that such bubble generation does occur withremarkable volume and facility at low rotative speeds and that thebubble volume and concentration increase as the speed of assemblrotation is increased, up to a critical point dependent upon nature anddensity of the cell charge beyond which the bubble propagation declinesas speed of assembly rotation increases. riving from whip assemblyrotation may be regulated and controlled within desired limits by meansof baffles and deflectors fixed: within the cell in a usual manner, andthe development of undesired vortex effect interiorly of the whipassembly, with the possibility of a consequent dead spot, may beobviated by the provision of a conical baffle 23, either ribbed orunribbed, upstanding fixedly from the floor of the cell I5 coaxiallywithin and surface-spaced from the orbit of said assembly. When tubularelements 22 are employed, rotation of the so-equipped whip assemblyinduces an air flow through each such element with a consequentsupplementing of the bubble-forming jet action at the element free ends.

The vortex-forming tendency of whip assem-- bly rotation in the cell l5induces a flow of froth inwardly about and towfard the flange 2| topossible resubmergence thereof within the pulp body, thus entailing apossible loss of efliciency through the necessity of reworking oncelevitated material, but an open-ended, annular collar 24 of suitablediameter and axial length may be fixedly suspended in any convenientmanner concentrically about said flange to intersect the pulp chargelevel and extend both above and below the same as a bafile limiting thespread of-the vortex effect in the pulp surface and damining. the frothaway from vortex influence-.-

Figure 3 illustrates a slight modification of the whip assembly abovedescribed, wherein the otherwise free, lower ends of the elements 22 arefixed in and serve to support an annulus 25 rotatable with and as a partof the assembly, while in Figure 4 is shownan alternative construction 0wherein the shaft 19 is extended to the base of Agitation of the cellcharge de-' mizing the bending stresses to which the elements 22 aresubject, and particularly adapting the whip assembly for use in certainheavy pulps. The modification according to Figure 5 utilizes theextended shaft l9 and plate 26 of Figure 4, but dispenses with theflange 2|, thus leaving the upper ends of the whips 22 free for reactionto the forces generated by assembly revolution, while in Figure 6 theextended shaft [9 of Figure 4 is furnished with a radially-armed spider2'! through the arm ends whereof the elements 22 engage at theirmidportions in any desired parallel or inclined relation with the axisof said shaft. Since changes, variations, and modifications in thespecific form, construction, and arrangement of the elements pertinentto practice of the improved method may be had without departing from thespirit of my invention,-I wish to be understood as being limited solelyby the scope of the appended claims, rather than by any details of theillustrative showing and foregoing description.

I claim as my invention:

1. A froth flotation apparatus comprising a pulp container open toatmospheric air at its top and having an outlet for froth, a shaftrotatably mounted vertically, impellers about said shaft spaced fromeach other circumferentially thereof and extending downwardly and beinof a length adapting the impellers to be partially submerged in pulpwith their upper portions projecting from the pulp, means for rotatingsaid shaft and causing the impellers to move in a circular path andthereby cause air under atmospheric pressure to move downwardly throughthe pulp along the impellers and then outwardly from the impellers andupwardly through the pulp, and an annular shield surrounding portions ofthe shaft and the impellers above and below the surface of the pulp andconstituting a barrier serving to prevent froth upon the surface of thepulp from being drawn downwardly through a vortex formed duringoperation of the apparatus.

2. A froth flotation apparatus comprising a pulp container open at itstop and having an outlet for pulp at one side, a shaft rotatably mountedvertically, impellers mounted about said shaft in circumferentiallyspaced relation to each other and consisting of downwardly divergingrods straight throughout their length and being of a length adapting theimpellers to be partially submerged in pulp with their upper portionsprojecting from the surface of the pulp; means for rotating said shaftand causing the impellers to move in a circular path and thereby causingair under atmospheric pressure to follow paths downwardly through thepulp along the rods and then move outwardly and upwardly through thepulp, and an annular shield disposed about portions of the shaft and theimpeller rods above and below the surface of the pulp and serving toprevent froth upon the surface of the pulp from being drawn downwardlythrough a vortex formed during operation of the apparatus.

3. A froth flotation apparatus comprising a pulp container open at itstop and having an outlet for froth at one side, a shaft rotatablymounted vertically, impeller rods mounted about said rod in spacedrelation to each other circumferentially thereof, said rods beingstraight and extending downwardly in diverging relation to each otherand of a length adapting them to be partially submerged in pulp withtheir upper portions projecting upwardly out of the pulp, means forrotating said shaft and thereby moving said impeller rods in a circularpath and causing air under atmospheric pressure to move downwardlythrough the pulp along the rods and then move outwardly from the rodsand upwardly through the pulp and form froth upon the surface of thepulp, an upwardly tapered conical baffle upon the bottom of saidcontainer disposed vertically in axial alignment with said shaft andsurrounded by said impeller rods and serving to eliminate a dead spot inthe pulp, and an annular shield surrounding portions of the shaft andthe rods below and above the surface of the pulp and serving to preventfroth from being drawn downwardly through a vortex formed duringoperation of the apparatus.

. PEARSON M. PAYNE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 278,985 Luck June 5, 1883 575,499Andersen Jan. 19, 1897 835,960 Leaver Nov. 13, 1905 901,808 HamiltonOct. 20, 1908 1,394,306 Hynes Oct. 18, 1921 1,736,073 Fagergren Nov. 19,1929 2,114,275 Murphy et a1 Apr. 12, 1938 2,385,679 Zacker Sept. 19,1944

